Fire alarm system



Aug. 25, 1936. F. REU: 2,052go57 AFIRE ALARM SYSTEM Aug. l:25, 1936. F.REID f 2,052,057

FIRE ALARM SYSTEM' Filed Nov. 7, 1929 2 sheets-Sheet 2 A rrr;

Patented Aug. l25, 11936 PATENT oFEiCE FIRE ALARM SYSTEM FrederickReid,- Neasden, London, England Application November 7, 1929, Serial No.405,472 In Great Britain January 4, 1929 6 Claims. (Cl. 1774352) Thisinvention relates to fire alarm systems and is applicable to analogous,systems such as arnbulance call systems so that whenever the expressioniireJ alarm system occurs herein it is to be understood as includingsuch analogous systems and the expression fire alarm is to includeanalogous calls.

Such systems are divided broadly into two main classes, namely, closedcircuit. systems in which the current supply is interrupted for thepurpose of giving a fire. alarm, and "open circuit systems in which theline circuit is completed for current to flow therein for the purpose ofgiving the fire call. The former systems in general are constructed onthe closed circuit metallic loop system, While the latter may be ofeither the metallic loop or earth return type.

The object of the invention is to improve the arrangement of opencircuit systems whereby they may be adequately and continuously orfrequently tested and to provide means for readily distinguishing firecalls from electrical faults.

Another object of the invention consists in the provision of means forfacilitating automatic routine testing in open circuit systems and otherdetails and arrangements hereinafter described or indicated.

The accompanying drawings illustrate one form of apparatus in accordancewith the invention. v l

Figure. l shows a diagram of an open circuit're alarm system'dnaccordance with the invention embodying an arrangement for automatic and'regular routine testing of each re alarm circuit.

Figures 2, 3 and 4 show parts of apparatus on an alarm box whereby asignal is transmitted, and

Figures 5, 6 and '7 show routine testing arrangements for use in suchcircuits.

When applying my invention to open circuit systems I may provide myimprovements in such systems independently of whether they are me-"inent now considered (as shown ior example in Figure 1).

As generally arranged the line is normally disconnected at -the firealarm bemand a fire signal is sent by connecting the line tothe earthreturn either temporarily or until ;eleased in some manner, or in`accordance with a definite numerical code. The defects of sucharrangements as hitherto adopted are:-

(1) That earth or electrical faults may cause false calls;

(2) That it is diflilcult to arrange for either a continuous. or'frequent test of the continuity of the line under conditions identicalwith working conditions.,

In order to remedy these defects of existing systems in accordance withthis inventions. suitable rectiiier is inserted in the earth return ormetallic return at each box, and is arranged in relation to the stationbattery so that normally no current will pass in the line, but when abox is pulled to` give a re alarm the connections to the rectifier arereversed` by suitable means'in order that the current may then pass toactuate the alarmv apparatus and preferably the rectifier is held in itsreversed condition by the locking of a cam or otherwise until releasedby a fireman or' responsible omcial. Such an arrangement is shown inFigures 2, 3 and 4 and comprises a camshaft a provided with a handle bwhich projects from the call box and is rotated in a counterclockwisesense to transmit an alarm signal. This reverses the circuit connectionsby relative .movement of contacts c and the shaft is held in itssignalling position locked by a spring controlled pawl d until releasedby a responsible omcial. Such an arrangement permits of the applicationof simple means for testing the line since it will be clear that byreversing the station battery the current may be passed through the lineat any desired time, the testing circuit including a suitable indicator(such as a milliammeter) to enable the observer to test whether thecurrent isof proper strength, in which case the line may be regarded a'ssatisfactory.

The use of a rectifier at the fire call point also provides a ready'means of distinguishing re calls from earth faults. In one arrangementof the station apparatus, for example, a relay is connected ineachcircuit to reverse the polarity of the line and cut off the i'ire alarmindicator in the operated position.

The reversal of the rectifier at the call point on' a` 4iire callcausesI the relay to operate like a trembler bell as current vcan onlyow when the relay is in the non-operated position. Pulses of current aretherefore sent through the fire alarm indicator which is preferably aslow acting type, causing it tobe actuated.

An earth'fult'causes the relay to operate remain in itsoperatedposition, cutting off the fire alarm indicator which inconsequence is not actuated.

Figure 1 shows one convenient arrangement of open circuit systemaccording to the invention, which, for the sake of simplicity, isarranged as an earth return system, although as above indicated theinvention is equally applicable to metallic return circuits. In Figure 1I have shown two lines connected to the main station, each line having acall box and each line having its indicator I, its indicator control orreversing relay 8, its jack I3 and resistance I5, and its set of camsprings 2I-26, inclusive. The alarm signal controlled by indicator l maybe common to a group of lines as shown as may also be relay I8,batteries 6n and 20, and signal I4 and jack I2 with its key I6. Asindicated a cam operates springs 2| to 25 at one time to disconnectbattery Se from the rst line and connect the test relay thereto whilesprings 2i to 25' are operated at another time by another cam todisconnect battery 6 from another line and connect test relay I8thereto. Normally. in such an arrangement the battery 6 has its positivepole connected via contact I0, indicator l, contacts i, resistance I5,by line to the box, contacts k, rectifier 4, contacts l to earth; andits negative pole via relay 8, contacts 9 and contacts I3 also to earth.

The rectifier 4 in the fire alarm box is normally connected so that nocurrent can ow to earth from the battery 6.

A fire call is made by pulling handle I which operates and locks cam 2and reverses contacts k and l on switch 2'a permitting current to flowfrom the positive pole of battery 6 through the normal line circuit andnew arrangement of contacts k and l to earth, returning through contactsI3, 9 and relay 8 to the negative pole of battery 6'. y

Relay 8 will operate and change over contacts 9 and III. Contacts 9 andIIJ reverse battery to line and as the rectier is now in inoperativecondition for this direction of current ow the current to line will besmall and relay 8 will restore when process is repeated. Relay 8therefore vibrates like a trembler bell sending pulses of unidirectionalcurrent through indicator l which is slugged or otherwise made slow tooperate. This will cause indicator le to operate giv-v ing a visual andaudible signal of a re call, the audible signal being made by theclosing of contact II on account of the operation of indicator 1*.

In the event of an earth fault on the line, relay 8 will operate andremain operated as current will ow through the earth fault even whenvthe battery is reversed. Contact III cuts oif the indicator 1 so -thatthe latter is not operated by the steady current. An earth fault willtherefore not give a re call. Plug I2 can be plugged into jack I3* togive a warning by the operation of indicator I4 when the re call pointhas been restored to normal. An adjustable resistance I5 can be employedi! desired to balance all lines to a common resistance (e. g. 500 ohms).A speaking key I6 and telephone I'I can be provided if desired and whenused a telephone such as T can be inserted into the line by means ofplug Y and jacks such as X and X if the fireman desires to converse withthe central omce as isv common practice. Y

When plug I2 is inserted in jack I3 on receipt of a nre call due to thereversal of rectier 4 at call-point, the negative pole of battery C isconnected via indicator I4, back contacts of key I6, tip of plug, shortspring of jack I3 to line, whilst the positive pole of battery isconnected via ring of plug and long spring of jack I3 to earth.

No current flows under these conditions as rectifier 4 has been reversedso that current can now only iiow from the line through the rectifier 4to earth when the line is connected to the positive pole of the battery.Indicator I 4l is therefore not operated until the rectier 4 has beenreset to normal by the reman at the call point.

The station attendant can, by throwing key I6, introduce a telephonetransmitter and receiver I'I into the circuit. y

'I'he testing may be performed by hand but I prefer to arrange for anautomatic testing to be carried out and where, as is usual, the systemwill include a number of boxes, an automatic routine test is preferablyprovided, it being understood that by routine tester I mean an automatictester which when set into operation will run round a set of circuitsand test each one individually. Obviously such routine test may beapplied in many different ways since basically the .rectiers provided inaccordance with the invention enable the lines to be tested under actualworking conditions.

In one particular construction, for example as shown in Figures 5,. 6and 7, I may provide a master clock e' which will close a contact, e. g.f', f2, f3, f4, say, once every1 15 minutes for the purpose of startingthe test and will then by means of ratchet wheel g' (stepped by theratchet lever system h of the electromagnet 7" energized by the closedcircuit), cause cams k', k2, k3, etc. which are on the same shaft as thewheel g' each to close a set of contacts l', l2, Z3, etc. whereby thedifferent circuits are reversed for testing. The cams are set at anglesto one another on the shaft in order that only one circuit is tested ata. time. The stepping of the wheel g' may be effected one tooth persecond until it has made one complete revolution. As soon as thestepping switch of a particular line operates to reverse the circuit,the fire alarm indicator for that line will be cut off, and one coil ofa testing (differential) relay will be connected to line with reversedbattery so that the current which then flows through the line will bebalanced against a current through the other coil of the testing(differential) relay, and if the current in the line is not equal to thestandard Working current within a prescribed margin the line will befaulty and a fault indicator will drop and, if necessary, a fault bellmay be made to ring.`

In another particular construction specially suitable for systems wherethe lines are to be tested at frequent intervals I employ a motordriving through a reduction gear to operate the test switches.

Figure 1 embodies one arrangement which may be used for the automaticand regular routine testing of each re circuit.

When springs 2|, 22, 23, 24, 25 by cams such as lc', k2, k3, etc.,Figure 7, are changed over the station battery 6 and fire indicatingapparatus are cut out of circuit and a testing battery 2Il with thepositive pole earthed (i. e. reversed with respect to station battery)is connected to the normal line circuit via one coil of a diilerentialrelay I8 and through'the other coil of I8` to a rectier I9 and aresistance 28 which exactly balances the line..resistance. Rectifier I!is introduced into the routine testing compensation cir- 75 cuit inorder to give a proper balance. vIl! the line is free from faults thedifferential relay Ilv ferential relay I8 from battery 2li respectivelylthrough rectifier i9, spring 2l, resistance 26 to earth, and spring 23,resistance i5", rectifier to earth, lthus giving rise to an unbalance,operating relay I8 and closing contact 28 which drops fault indicator 21associated with the line being tested. A contact 29 associated with eachline is broken when the, fire indicator 'I is actuated to prevent :firecalls also actuating the fault indicator.

`Each line is provided with a set ofsprings 2 I, 22, 23, 24. 25. Thesesets are operated in succession by cams of the kind shown in Figure 7driven for example by a ratchet drive operated by a magnet controlledfrom a clock.

It is proposed to arrange a group of ten lines on one cam assembly andarrange to test each line in turn one every minute.

The period of test need not exceed one second so that the testing wouldnot delay any call .for more than one second and on the average only onecall in sixty would be so delayed.

The mechanical arrangement forr driving the routiner and the period oftest are ofcourse subject to wide variation in accordance with therequirements of any system.

As previously p'ointed out the mechanical devvices illustrated inFigures 2 to '1, inclusive, are

merely-one form of well known mechanism which may be utilized. The clockcontrolled sequence switches such as indicated in Figures 5, 6 and 'Iare well known in the telephone art and merely consist of a series ofcams on a shaft which shaft is rotated by a magnet operating a pawl andratchet and controlled from contacts on an electric clock such as aprogram clock. The detailed mechanisms are not a part of my invention.

It will be understood that the details of the testing arrangementA thusgiven are purely by way of illustration as obviously the. periods oftest may be varied and the particular mecha.- nisms employed forautomatically bringing each line into test may also be modified withinwide limits, the essential feature of the invention being that in anopencircuit system the line or lines may be subjected to testautomatically and as frequently as may be considered desirable.

In the foregoing descriptiony it is assumed that the line will normallybe connected to earth through a rectifier connected, for example, so

. that current can only pass to earth when the line .is negative toearth but some features of the inaccordance with any practicalrequirements thatV may have to be'fulfilled.

Further, any convenient form of rectier may be employed in accordancewith the invention, although I have found that very satisfactoryresultsmay bei-obtained by the use of copper oxide rectiers:

I claim c 1. An open circuit fire alarm system comprising a cali point,a central station, an electric circuit connecting the two, .a source ofcurrent in said circuit. a rectifier at said call point sc ar- 5 rangedin said circuit vthat no currentI normally flows, means at said calipoint for reversing the connections to the rectifier in order to cause asignalling current to flow over said circuit, y,and receiving meansatthe station operated, under 10 -the influence of said signallingcurrent, temporarily to reverse the connections of said source to theline to temporarily stop the flow of signalling current thereover, saidreceiving means intermittently operated responsive to said sourceconnec- -l5 tions reversal to give a fire alarm in case the current flowis stopped by said reversal and operated steadily to prevent a firealarm responsive to said.' reversal in case the flow of current is dueto causes other than the reversal of the rectifier. 20 connections andtherefore current flow is not stopped by said reversal.

2. In a fire alarm system, a plurality of lines connecting call pointsto a central station, a battery and alarm equipment connected to each 25line atthestation, a rectifier in each line at the call point;` normallyconnected to prevent current. flowing` from' the battery over suchline,y means at each call point for reversing the connection of therectifier of that line to permit current to 30 flow to operate the alarmequipment of that line, test equipment for successively connecting abattery of reversed polarity to the lines, 'arelay in the test equipmentoperated only in case of a fault in the line, an indicator controlled bysaid 35 relay, and means controlled'by the alarm equipment vof a linefor preventing operation of the test equipment indicator if it isassociated with that line when the rectifier thereof is reversed.

3. In a fire alarm system, a line connecting a rcall point to a centralomce, a batterygand a signal connected to the line at the omc "aArectifier in the line at the call point normally zrcventing any currentfrom flowing from tha-battery over the line to operate the signal,means' atthe call a5 point for reversing the connections oi therectifier to the line to thereby permit current to flow over the line tooperate the signal, another signal at the omce, means for disconnectingthe first signal from the line and connecting the second ,50 signalthereto, said second signal so connected toA the line as to beinoperative when the rectifier is reversed, said second signal operatedresponsive to the reversal of the rectier-to its normal connection tothe line. 1; 55

4. In a nre alarm system, aline connected between a call point andacentral station, a rectiiler in the line at the station, a batteryconnected in the line at the central station, said rectiiier normallypreventing current flow from the batce tery over the line, a controlrelay and an alarm relay connected to the line at the station, means atthe call point for reversing the rectiner to transmit a nre alarm bycausing a current to flow in the line, said control relay operatedresponsive 65 to said current flow to reverse the connections oi saidbattery in the line to test the line for accidental grounds, saidcontrol relay continuously operated responsive to an accidental groundon the line to prevent any further operation of said V70 alarm relay andintermittently operated in case the line is normal to control the alarmrelay.

5. In a re alarm system, a line connecting a main station to a callpoint,-a rectifier in the line at the call point and a battery connectedthereto 7 battery to the line, said relay operated steadily if a directground is present on the line when the battery is so reversed and saidrelay operated intermittently when the battery is reversed re sponsiveto said current flow if no direct ground is present on the line, and analarm controlled by said relay when intermittently operated.

6. In a re alarm system, a line leading from a central station to a callpoint, alarm equipment and a source of current supply at the station forsaid line. a rectifier in said line at the call point normallypreventing operation of the equipment. means at the call point forreversing the connections of the rectifier to its line, means in thestation responsive to the reversal of the rectier for reversing theconnections of said source to the line, means at the station operatingin one manner responsive to said reversal of the source and tosaidreversal of the rectifier connections to cause an operation of saidalarm equipment, said means at the station operating in another mannerresponsive to said reversal of the source to prevent operation of thealarm equipment for such line in case an accidental ground is present onthe line.

FREDERICK REID.

